Certain pesticidal agents are inactivated by ultra-violet radiation from the sun. Because those pesticidal agents are useful for the control of pests and are applied in areas where they will be exposed to ultraviolet radiation, there is a need for photostable compositions containing those agents.
To prevent ultraviolet inactivation of pesticidal agents, compositions have been prepared which contain ultraviolet absorbers and/or reflectors and a pesticidal agent.
U.S. Pat. No. 3,541,203 describes a protected virus composition for insect control. The preferred composition includes a virus, an actinic light absorbing material and a polymeric binder material. However, the process used to prepare the preferred compositions of U.S. Pat. No. 3,541,203 requires the use of toxic materials and numerous washing steps with flammable solvents thus making it unsuitable for commercial manufacture.
U.S. Pat. No. 4,948,586 discloses a microencapsulated insecticidal pathogen. Four microencapsulated compositions are shown to decrease the photoinactivation of Autographa californica NPV. However, the microencapsulated compositions retain only from 30.7 to 71.43% of the original activity upon exposure to sunlight. U.S. Pat. No. 4,948,586 discloses a method of preparing microencapsulated insecticidal pathogens which has numerous steps and is both time-consuming and laborious. It is apparent that neither the process, nor the microencapsulated insecticidal pathogens, described in U.S. Pat. No. 4,948,586, are entirely satisfactory for providing a product stable to ultraviolet radiation.
U.S. Pat. No. 5,560,909 discloses a process for the preparation of insecticidal compositions which requires the modification of the charge of a charged polymer to precipitate the polymer and entrap the insecticide. However, this process is not entirely satisfactory because a small amount of the functional groups on the polymer will remain charged in the final product, resulting in a less efficacious product.
EP 697170-A1 discloses a process for the preparation of coated pesticidal agents which requires that the coating polymer be completely dissolved and which adjusts the pH of the coating solution to attain such dissolution. Unfortunately, such dissolution reduces some of the desirable properties of the coating polymer, resulting in a less efficacious product.
The present invention comprises an improved process for the preparation of a coated pesticidal matrix, which process comprises: a) preparing an aqueous mixture comprising a pesticidal agent, a pH-dependent polymer and water, wherein the pH is below the solubilization pH of the polymer; and b) drying the aqueous mixture to produce the coated pesticidal matrix. The aqueous mixture optionally includes a plasticizer, an ultraviolet protector, an activity enhancer and/or a glidant thus resulting in their presence in the coated pesticidal matrix. Preferably, the pesticidal agent is a particulate chemical insecticide or a viral, bacterial or fungal insecticidal pathogen.
The present invention also comprises wettable powder pesticidal compositions which comprise coated pesticidal matrices, together with suitable carriers.
The present invention further comprises a method for improving the residual control of a pest comprising the application of a matrix made by the process of this invention.
It is an object of the present invention to provide a coated pesticidal matrix which retains the desirable properties of the coating polymer and thus retains a significant amount of its original pesticidal activity after exposure to ultra-violet radiation.
It is also an object of the present invention to provide an improved process for the preparation of a coated pesticidal matrix under mild conditions which avoid degradation of the pesticidal agent.
Other objects of this invention will be apparent to those skilled in the art from the following description and the appended claims.